Field-free Spin-Orbit Torque Perpendicular Magnetization Switching Induced by Metallic Multilayers

The realization of the all-electrical manipulation of perpendicular magnetization switching is essential for next-generation information storage technologies and spintronic devices. Current-induced spin-orbit torque (SOT) has attracted tremendous research interest. However, this approach usually relies on external magnetic field to achieve deterministic switching, which greatly limits SOT devices moving toward practical applications. Here, we report the measurement of SOT from the [Pt/Au] multilayer with composition gradient along the thickness direction. The multilayer exhibits a much larger SOT efficiency than pure Pt, and current-induced field-free magnetization switching has been realized in Co/[Pt/Au] heterostructures. Anomalous Hall resistance loop shift measurements indicate that the [Pt/Au] multilayer can produce spin current with z-direction polarization. Moreover, the results of the control experiments show that the Pt/Au interface is the primary cause of the z-direction polarized spin current for triggering field-free switching, whereas the compositional gradient effect is peripheral. We speculate that the field-free switching originates from the synergetic interface effect and Dzyaloshinskii-Moriya interaction. Our work not only paves the way for SOT devices toward practical application but also provides novel insights into the mechanisms governing current-induced deterministic perpendicular magnetization switching.